sediments in salt marshes can allow for 

 long-term storage of materials in the 

 soils. Of course, the extent to which 

 one can get rid of sewage in this fash- 

 ion will depend on how much sedimenta- 

 tion is taking place. 



In the Massachusetts marsh, the ac- 

 cretion rate was a matter of centimeters 

 per year, and in the Georgia marsh, the 

 sedimentation rate is considerably less, 

 about a millimeter per year. In Mass- 

 achusetts, about 80% to 96% of the ni- 

 trogen added in the sewage sludge fer- 

 tilizer was retained in the marsh sedi- 

 ment, whereas in our study we can only 

 account for 60% of the nitrogen that we 

 added in sewage sludge; the rest was 

 probably washed out by the tides. Some 

 of the nitrogen could have been denitri- 

 fied or volatilized as ammonia off the 

 sediment surface. The Massachusetts 

 group found that the waterlogged sedi- 

 ments in the marsh soils apparently can 

 get rid of significant amounts of nitro- 

 gen through denitrification. On the 

 other hand, the accumulation of toxic 

 materials in marsh sediments will have 

 long-term effects which we do not know 

 much about. The marsh plants can pump 

 certain ions, which might include toxic 

 compounds, from the soil to the estua- 

 rine water. We also do not have any 

 idea about the maximum loading rate be- 

 yond which the marsh system will begin 

 to deteriorate. 



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